The present invention relates to a transimpedance amplifier using current feedback through a resistor and serving to convert an input current into an output voltage.
A transimpedance amplifier of this kind is described, for example, in an article by Y. Netzer in the journal "EDN", Sept. 20, 1980, pp. 161 to 164. Transimpedance amplifiers are well suited for use as low-noise peramplifiers of optical receivers in which the light-sensitive detector is a PIN photodiode.
It is known that, for such applications, the value of the feedback resistor of the transimpedance amplifier should be as large as possible to minimize the amplifier's input noise, which is determined essentially by the noise current of the resistor, and that the product of the feedback resistance and the amplifier's input capacitance should be as small as possible to obtain maximum bandwidth. (The bandwidth is approximately proportional to A/(R.multidot.C), where A is the open-loop gain, R is the value of the feedback resistor and C is the amplifier's input capacitance).
Thus, a large feedback resistance improves the noise characteristics but reduces the bandwidth, so that it is considered difficult to develop amplifiers which have both a wide bandwidth and low input noise.
From "Electronics Letters", Vol. 15, No. 20, pp. 650 to 652, a transimpedance amplifier is known which has a considerable bandwidth, namely 112 MHz, but, because of the small feedback-resistor value of 5.1 k.OMEGA., exhibits too high input noise and, thus, too low sensitivity to meet the requirements placed on optical receivers.